Geographic variation in offspring size of a widespread lizard (Takydromus septentrionalis): importance of maternal investment

Geographic variation in offspring size is widespread, but the proximate causes of this variation have not yet been explicitly determined. We compared egg size and egg contents among five populations of a lizard (Takydromus septentrionalis, Günther, 1864) along a latitudinal gradient, and incubated eggs at two temperatures to determine the influence of maternal investment and incubation temperature on offspring size. The mean values for female size and egg size were both greater in the two northern populations (Chuzhou and Anji) than in the three southern populations (Lishui, Dongtou, and Ningde). The larger eggs were entirely attributable to the body size of females in the Anji population, but their increased size also stemmed from further enlargement of egg size relative to female body size in Chuzhou, the northernmost population sampled in this study. Eggs of the Chuzhou population contained more yolk and less water than those of southern populations. Despite the lower lipid content in the yolk, eggs from the Chuzhou population had higher energy contents than those from the two southern populations, owing to the larger egg size and increased volume of yolk. Hatchling size was not affected by incubation temperature, but differed significantly among populations, with hatchlings being larger in the Chuzhou population than in the other populations. Our data provide an inference that oviparous reptiles from cold climates may produce larger offspring, not only by increasing egg size but also by investing more energy into their eggs. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 59–67.     

THE EVOLUTION OF MATERNAL INVESTMENT IN LIZARDS: AN EXPERIMENTAL AND COMPARATIVE ANALYSIS OF EGG SIZE AND ITS EFFECTS ON OFFSPRING PERFORMANCE

I used comparative and experimental analysis of egg size in a Sceloporus lizard to examine a fundamental tenet of life-history theory: the presumed trade-offs among offspring number, offspring size, and performance traits related to offspring size that are likely to influence fitness. I analyzed latitudinal and elevational patterns of egg life-history characteristics among populations and experimentally manipulated egg size and hatchling size by removing yolk from the eggs to examine the causal bases of population differences in offspring traits. Mean clutch size among populations increased to the north (seven vs. 12 eggs/clutch, California vs. Washington), whereas egg size decreased (0.65 g vs. 0.40 g). The elevational patterns in southern California paralleled the latitudinal trends. Several offspring life-history traits that are correlated with egg size also varied geographically; these traits included incubation time, hatchling size, growth rate, and hatchling sprint performance. Hatchling viability of experimentally reduced eggs was remarkably high (~70%), even when up to 50% of the yolk was removed. The experimentally reduced eggs and hatchlings demonstrated the degree to which size influences each of the offspring life-history traits considered. Northern eggs hatched sooner, in part because of their small size. Though growth rate is allometrically related to size within each population (i.e., smaller hatchlings grow faster on a mass-specific basis), population differences in growth rate, as measured in the laboratory, are likely to reflect genetic differentiation in the underlying physiology of growth. Moreover, smaller juveniles, because of experimental reduction, had slower sprint speeds than larger juveniles. The slower sprint speed of hatchlings from Washington compared to hatchlings from California is thus largely due to the fact that eggs are smaller in the Washington population. These results provide a basis for interpreting the evolutionary divergence of the suite of traits involved in the evolution of maternal investment per offspring in lizards. For example, evolutionary divergence in some offspring traits functionally related to size (e.g., sprint speed) may be constrained, relative to traits that are determined by other aspects of development or physiology (e.g., growth). I also discuss issues relating to the evolution of maternal investment that could be tested in laboratory and natural populations using experimentally reduced offspring.     

Evolutionary divergence in life history traits among populations of the Lake Malawi cichlid fish Astatotilapia calliptera

During the early stages of adaptive radiation, populations diverge in life history traits such as egg size and growth rates, in addition to eco‐morphological and behavioral characteristics. However, there are few studies of life history divergence within ongoing adaptive radiations. Here, we studied Astatotilapia calliptera, a maternal mouthbrooding cichlid fish within the Lake Malawi haplochromine radiation. This species occupies a rich diversity of habitats, including the main body of Lake Malawi, as well as peripheral rivers and shallow lakes. We used common garden experiments to test for life history divergence among populations, focussing on clutch size, duration of incubation, egg mass, offspring size, and growth rates. In a first experiment, we found significant differences among populations in average clutch size and egg mass, and larger clutches were associated with smaller eggs. In a second experiment, we found significant differences among populations in brood size, duration of incubation, juvenile length when released, and growth rates. Larger broods were associated with smaller juveniles when released and shorter incubation times. Although juvenile growth rates differed between populations, these were not strongly related to initial size on release. Overall, differences in life history characters among populations were not predicted by major habitat classifications (Lake Malawi or peripheral habitats) or population genetic divergence (microsatellite‐based F_ST). We suggest that the observed patterns are consistent with local selective forces driving the observed patterns of trait divergence. The results provide strong evidence of evolutionary divergence and covariance of life history traits among populations within a radiating cichlid species, highlighting opportunities for further work to identify the processes driving the observed divergence.     

Egg size, composition and offspring quality in some Alcidae (Aves: Charadriiformes)

The composition of fresh and fully developed (pipping) eggs of four alcids, Razorbill, Common guillemot, Brünnich's guillemot and Atlantic puffin was examined. There were no differences in egg composition between the semi-precocial Atlantic puffin and the three species with "intermediate" developmental patterns. The absolute amount of yolk increased with egg size in fresh eggs, and the relative amount remained constant with egg size for Common guillemot and Razorbill, but decreased in the Atlantic puffin. In fully developed eggs chick weight and egg weight were closely correlated, and this was due mainly to larger eggs producing chicks with larger yolk reserves. Under some conditions chicks from larger eggs do better than those from smaller eggs. Several factors influence egg size; a comparison of first and replacement eggs laid by the same females showed that a maternal effect accounted for 60–90% of the variance in egg-size and that laying date accounted for most of the remaining variance.     

Geographic variation in reproductive traits and trade-offs between size and number of eggs of the Chinese cobra (Naja atra)

We collected gravid Chinese cobras (Naja atra) from one island (Dinghai) and three mainland (Yiwu, Lishui and Quanzhou) populations in south‐eastern China to study geographical variation in female reproductive traits and the trade‐off between the size and number of eggs. We then conducted an common experiment on cobras from two of the four populations to further identify factors contributing to the observed trade‐offs. The mean size (snout–vent length) of the smallest five reproductive females increased with increasing latitude. Oviposition occurred between late June and early August, with females from the warmer localities laying eggs earlier than those from the colder localities. Maternal size was a major determinant of the reproductive investment in all populations, with larger females producing not only more but also larger eggs. Clutch size was more variable than egg size within and among populations. The observed geographical variation in clutch size, egg size, clutch mass and post‐oviposition body condition was not a simple consequence of variation in maternal size among populations, because interpopulation differences in these traits were still evident when the influence of maternal size was removed. The upper limit to reproductive investment was more likely to be set by the space availability in the island population, but by the resource availability in the three mainland populations. Trade‐offs between size and number of eggs were detected in all populations, with females that had larger clutches for their size having smaller eggs. Egg size at any given level of relative fecundity differed among populations, primarily because of interpopulation differences in the resource availability rather than the space availability. Except for the timing date of oviposition and the mean size of the smallest five reproductive females, all other examined traits did not vary in a geographically continuous trend. The common garden experiment, which standardized environmental factors, synchronized the timing date of oviposition, but it did not modify the conclusion drawn from the gravid females collected from the field. The observed geographical variation in the female reproductive traits could be attributed to the consequence of the effects of either proximate or ultimate factors. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 27–40.     

Body size-specific maternal effects on the offspring environment shape juvenile phenotypes in Atlantic salmon

Positive associations between maternal investment per offspring and maternal body size have been explained as adaptive responses by females to predictable, body size-specific maternal influences on the offspring’s environment. As a larger per-offspring investment increases maternal fitness when the quality of the offspring environment is low, optimal egg size may increase with maternal body size if larger mothers create relatively poor environments for their eggs or offspring. Here, we manipulate egg size and rearing environments (gravel size, nest depth) of Atlantic salmon (Salmo salar) in a 2 × 2 × 2 factorial experiment. We find that the incubation environment typical of large and small mothers can exert predictable effects on offspring phenotypes, but the nature of these effects provides little support to the prediction that smaller eggs are better suited to nest environments created by smaller females (and vice versa). Our data indicate that the magnitude and direction of phenotypic differences between small and large offspring vary among maternal nest environments, underscoring the point that removal of offspring from the environmental context in which they are provisioned in the wild can bias experimentally derived associations between offspring size and metrics of offspring fitness. The present study also contributes to a growing literature which suggests that the fitness consequences of egg size variation are often more pronounced during the early juvenile stage, as opposed to the egg or larval stage.     

Growth of yellow-headed blackbird Xanthocephalus xanthocephalus nestlings in relation to maternal body condition, egg mass, and yolk carotenoids concentrations

Condition‐dependent resource allocation to eggs can affect offspring growth and survival, with potentially different effects on male and female offspring, particularly in sexually dimorphic species. We investigated the influence of maternal body condition (i.e., mass‐tarsus residuals) and two measures of female resource allocation (i.e., egg mass, yolk carotenoid concentrations) on nestling mass and growth rates in the polygynous and highly size dimorphic yellow‐headed blackbird Xanthocephalus xanthocephalus. Egg characteristics and carotenoid concentrations were obtained from the third‐laid egg of each clutch and were correlated with the mass and growth rates of the first two asynchronously hatched nestlings. Maternal body condition was associated with the growth of first‐hatched, but not second‐hatched nestlings. Specifically, females in better body condition produced larger and faster growing first‐hatched nestlings than females in poorer body condition. As predicted for a polygynous, size‐dimorphic species, females that fledged first‐hatched sons were in better body condition than females that fledged first‐hatched daughters. Associations between egg mass, yolk carotenoid content, and nestling growth were also specific to hatching‐order. Egg mass was positively correlated with the mass and growth rates of second‐hatched nestlings, and yolk concentrations of β‐carotene were positively correlated with second‐hatched nestling mass. Surprisingly, the relationship between yolk lutein and hatchling growth differed between the sexes. Females with high concentrations of yolk lutein produced larger and faster growing first‐hatched sons, but smaller first‐hatched daughters than females with lower lutein concentrations. Mass and growth rates did not differ between first‐ and second‐hatched nestlings of the same sex, despite asynchronous hatching in the species. Results from this study suggest that maternal body condition and the allocation of resources to eggs have carotenoid‐, sex‐, and/or hatch‐order‐specific effects on yellow‐headed blackbird nestlings.     

Size‐dependent reproductive success of wild zebrafish Danio rerio in the laboratory

Size‐dependent reproductive success of wild zebrafish Danio rerio was studied under controlled conditions in the laboratory to further understand the influence of spawner body size on reproductive output and egg and larval traits. Three different spawner size categories attained by size‐selective harvesting of the F₁‐offspring of wild D. rerio were established and their reproductive performance compared during a 5 day period. As to be expected, large females spawned more frequently and had significantly greater clutch sizes than small females. Contrary to expectations, small females produced larger eggs when measured as egg diameter with similar amounts of yolk compared to eggs spawned by large spawners. Eggs from small fish, however, suffered from higher egg mortality than the eggs of large individuals. Embryos from small‐sized spawners also hatched later than offspring from eggs laid by large females. Larval standard length (L_S)‐at‐hatch did not differ between the size categories, but the offspring of the large fish had significantly larger area‐at‐hatch and greater yolk‐sac volume indicating better condition. Offspring growth rates were generally similar between offspring from all size categories, but they were significantly higher for offspring spawned by small females in terms of L_S between days 60 and 90 post‐fertilization. Despite temporarily higher growth rates among the small fish offspring, the smaller energy reserves at hatching translated into lower condition later in ontogeny. It appeared that the influence of spawner body size on egg and larval traits was relatively pronounced early in development and seemed to remain in terms of condition, but not in growth, after the onset of exogenous feeding. Further studies are needed to explore the mechanisms behind the differences in offspring quality between large‐ and small‐sized spawners by disentangling size‐dependent maternal and paternal effects on reproductive variables in D. rerio.     

Geographic variation in hatchling size in an oviparous skink: effects of maternal investment and incubation thermal environment

Geographic variation in offspring size can be viewed as an adaptive response to local environmental conditions, but the causes of such variation remain unclear. Here, we compared the size and composition of eggs laid by female Chinese skinks (Plestiodon chinensis) from six geographically distinct populations in southeastern China to evaluate geographic variation in hatchling size. We also incubated eggs from these six populations at three constant temperatures (24, 28 and 32 °C) to evaluate the combined effects of incubation temperature and population source on hatchling size. Egg mass and composition varied among populations, and interpopulation differences in yolk dry mass and energy content were still evident after accounting for egg mass. Population mean egg mass and thus hatchling mass were greater in the colder localities. Females from three northern populations increased offspring size by laying larger eggs relative to their own size. Females from an inland population in Rongjiang could increase offspring size by investing relatively more dry materials and thus more energy into individual eggs without enlarging the size of their eggs. The degree of embryonic development at oviposition was almost the same across the six populations, so was the rate of embryonic development and thus incubation length at any given temperature. Both incubation temperature and population source affected hatchling traits examined, but the relative importance of these two factors varied between traits. Our data show that in P. chinensis hatchling traits reflecting overall body size (body mass, snout‐vent length and tail length) are more profoundly affected by population source. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 283–296.     

Effects of egg size and composition on the size, quality and survival of lapwing Vanellus vanellus chicks

The influence of egg size and composition on the size, quality and survival of lapwing chicks was examined on two farmland study sites in the Midland Valley of Scotland. Eggs comprised 33.1% yolk, 61.3% albumen and 5.6% shell. Whereas the yolk and shell proportions decreased with increasing egg size, the albumen proportion increased. Most variation in egg size was attributable to differences between females but was also influenced by clutch number (eggs in replacement clutches on the rough grazing, but not the arable, site were smaller), clutch size (eggs were smaller in smaller clutches), maternal body condition (females in good condition produced larger eggs) and habitat (since females on the arable site fed more successfully, they were in better condition and laid larger eggs). Chick size, weight and survival were all influenced by egg size. The incubation period varied between 21 and 28 days (mean = 25.2) and was shorter in clutches laid later in the season.     

Egg size and composition in Ceratoserolis (Crustacea: Isopoda) from the Weddell Sea

Summary Samples of ovigerous female Ceratoserolis trilobitoides carrying newly spawned (stage A1) eggs in the marsupium were obtained from Borge Bay; Signy Island (South Orkney Islands), the continental shelf near Elephant Island (South Shetland Islands), and two sites in the inner Weddell Sea. The dry mass of a newly spawned egg was greater at the inner Weddell Sea sites even when the larger size of the females from the Weddell Sea and the positive relationship between egg size and female size were taken into account. Larger eggs contained more yolk, and there was a slight but significant tendency for larger eggs to have a lower percentage nitrogen content. Eggs from Ceratoserolis meridionalis were smaller in size than sympatric Ceratoserolis trilobitoides, but of similar composition. The reason for a greater investment per egg by females at higher latitudes is not clear, but it may be related to a slightly longer development period, itself associated with the lower water temperatures in the inner Weddell Sea.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Larger eggs at lower water temperature as a measure to assure effective hatchling size in the landlocked form of Ayu, <Emphasis Type="Italic">Plecoglossus altivelis</Emphasis>

Egg size is a critical life-history trait in which maternal investment is optimized to maximize maternal fitness. The adaptive significance of variable egg size among spawning groups of Ayu (Plecoglossus altivelis) landlocked in the Lake Biwa system was examined through field investigations and rearing experiments. Observed egg size variations were explained by the water temperature around spawning grounds established near the mouths of inlet streams. Two typical streams with different incubation temperatures showed similar maternal body sizes and hatchling sizes, but eggs attached to the stream bed were larger in the colder stream. An experiment that used eggs from a single clutch showed that a smaller hatchling size was obtained with a lower incubation temperature, indicating that the effect of differences in egg size on hatchling size can be canceled out by variations in incubation temperature. In general, larvae that are less than a certain threshold of effective body size are not expected to be assured of early success among conspecifics competing for foods. It is proposed that environments in which the incubation temperature varies favor variability in egg size to ensure that sufficient food is accessible to larvae.     

Maternal body condition influences magnitude of anti-predator response in offspring

Organisms exhibit plasticity in response to their environment, but there is large variation even within populations in the expression and magnitude of response. Maternal influence alters offspring survival through size advantages in growth and development. However, the relationship between maternal influence and variation in plasticity in response to predation risk is unknown. We hypothesized that variation in the magnitude of plastic responses between families is at least partly due to maternal provisioning and examined the relationship between maternal condition, egg provisioning and magnitude of plastic response to perceived predation risk (by dragonfly larvae: Aeshna spp.) in northern leopard frogs (Lithobates pipiens). Females in better body condition tended to lay more (clutch size) larger (egg diameter) eggs. Tadpoles responded to predation risk by increasing relative tail depth (morphology) and decreasing activity (behaviour). We found a positive relationship between morphological effect size and maternal condition, but no relationship between behavioural effect size and maternal condition. These novel findings suggest that limitations imposed by maternal condition can constrain phenotypic variation, ultimately influencing the capacity of populations to respond to environmental change.     

Mothers influence offspring body size through post-oviposition maternal effects in the redbacked salamander, Plethodon cinereus

In the terrestrial salamander (Plethodon cinereus), previous work has shown that mothers body size is positively correlated to offspring size at the time of hatching even after controlling for the effects of egg size. This study was designed to determine whether maternal body size affects offspring size via pre-oviposition factors (e.g., yolk quality, jelly coat composition, or maternal genes) or post-oviposition factors (e.g., parental care behaviors, parental modification of environment). Gravid females were captured and induced to lay eggs in experimental chambers in which the environment was standardized. Fifteen clutches were exchanged, or cross-fostered, between female pairs differing in body size. Ten females whose eggs were taken away and then returned served as controls for the crossing treatment. Foster mothers did not significantly differ from control mothers in the time spent with eggs, body position, or number of egg movements during brooding. Average egg mass measured midway through development was not significantly correlated to the body size of either the genetic or foster mother, but was correlated to pre-oviposition oocyte size. At hatching, offspring body length was positively correlated to egg size and the foster mothers body size. This correlation suggests that in P. cinereus post-oviposition maternal effects have a greater impact on offspring size than other maternal factors incorporated into the egg prior to oviposition. While our study showed that larger mothers moved their eggs less often and tended to spend more time in contact with their eggs, further work needs to be done to identify the specific mechanisms through which larger mothers influence the body size of their offspring. This is the first experimental demonstration of post-oviposition maternal effects for any amphibian with parental care.     

Egg yolk carotenoids in relation to habitat and reproductive investment in the great tit Parus major

Maternal allocation of antioxidants to egg yolk has been shown to affect early embryonic development and nestling survival. In environments with high levels of anthropogenic pollution, antioxidants (such as carotenoids) are important to protect the body from elevated oxidative stress. Thus, female allocation of antioxidants to yolk may be traded off against self-maintenance. Here we investigate maternal reproductive investment with respect to yolk carotenoid content and composition in relation to subsequent female condition and carotenoid status in urban and rural great tits Parus major. We found no differences between the urban and rural populations in total yolk carotenoids, egg mass, clutch size, hatching success, or female carotenoid status. Interestingly, however, rural eggs contained more zeaxanthin, a more potent antioxidant than lutein, which suggests that rural embryos have better antioxidant protection than urban embryos. Whether rural females actively transfer more zeaxanthin to the yolk or whether it passively reflects differences in dietary access or uptake needs to be further investigated. This highlights the importance of carotenoid identity and composition in future studies of carotenoid physiology, ecology, and signaling.     

Interpopulational egg-size variation of a landlocked Rhinogobius goby related to the risk of larval starvation

Reproductive characteristics of a landlocked goby, Rhinogobius sp. (the orange form), in the Lake Biwa water system were compared between the fluvial-lacustrine and lacustrine populations to show the relationship of the egg size to the risk of larval starvation. The comparison of both oocytes in the ovaries and spawned eggs showed that egg size is larger in the fluvial-lacustrine population than in the lacustrine population. Although females of the two populations spawn eggs of the same number as a function of their body size, those of the fluvial-lacustrine population spawn larger eggs even in relation to their body size by investing more in reproduction than those of the lacustrine population. A positive correlation was experimentally shown between the egg size and larval starvation tolerance. Most larvae of the fluvial-lacustrine population (>2 days old) had exhausted their yolk during their larval drift downstream to the lake, indicating that larvae severely suffer from starvation. Egg-size variation between the two populations seemed to be the result of adaptation to the different life cycles, in which the fluvial-lacustrine population confronts the risk of larval starvation, whereas the lacustrine population seems safe from such risk of starvation.     

Experimental test of the effect of maternal hormones on larval quality of a coral reef fish

Maternal hormones can play an important role in the development of fish larvae. Levels of the stress hormone, cortisol, in females are elevated by social interactions and transferred directly to the yolk of eggs, where they may influence developmental rates. In some vertebrates, prenatal exposure to high levels of testosterone determine early growth rates, social status and reproductive success. The present study examined whether post-fertilization exposure of eggs of the tropical damselfish, Pomacentrus amboinensis (Pomacentridae), to natural levels of cortisol or testosterone directly affects larval morphology at hatching. Maternal and egg levels of cortisol and testosterone varied widely among clutches of eggs from local populations around Lizard Island on the Great Barrier Reef. The morphology of larvae produced by these local fish populations also varied widely and differed significantly among sites (e.g., standard length: 2.6–3.4 mm; yolk sac area: 0.01–0.13 × 10⁻² mm²). Laboratory experiments showed that elevated cortisol levels in the egg reduced larval length at hatching, while slight elevations in testosterone increased yolk sac size. The influence of testosterone, and to a smaller extent cortisol, on larval morphology differed among egg clutches. These differences were partly explained by differences in initial egg hormone levels. Morphological changes induced by experimental hormonal regimes encompassed the entire range of variability in body attributes found in field populations. It is unclear whether cortisol influences growth alone or development rate or both. Testosterone appears to influence yolk utilization rates, and has no significant effect on growth, in contrast to its role in later developmental stages. Maternally derived cortisol and testosterone are important in regulating growth, development, and nutritive reserves of the embryo and larvae of this fish species. Factors that influence the maternal levels of cortisol and testosterone may have a major impact on larval mortality schedules and, therefore, on which breeding individuals contribute to the next generation. Received: 19 August 1998 / Accepted: 16 November 1998     

Relationship between reproductive resource allocation and resource capacity in the matriphagous spider, <Emphasis Type="Italic">Chiracanthium japonicum </Emphasis>(Araneae: Clubionidae)

Females of the Japanese foliage spider, Chiracanthium japonicum, are eaten by their offspring at the end of the maternal care period. To examine the patterns of allocation of maternal investment to their offspring associated with female resource capacity, the amounts of female body reserves accumulated before oviposition, reproductive components at the egg-production phase and those at the matriphagy phase were measured using an artificial breeding nest. Regardless of size, female bodies were completely consumed by the offspring, and larger females, i.e. those having larger reserves, produced a larger number of offspring, but not larger offspring. Furthermore, the proportion of reserves allocated to egg production was not affected by the total amount of the reserves, which indicated that the females systematically divided the resources for individual offspring between egg yolk and food for the growth and survival of the offspring. These results suggest that C. japonicum females adjust egg production to their own resource capacity so that they can achieve an investment per individual offspring which is not dependent on resource capacity. Electronic Publication     

Variation in body size in the giant rhinoceros beetle Trypoxylus dichotomus is mediated by maternal effects on egg size

1. The egg size of insects can vary depending on maternal body size or resource status, and it may influence offspring body size by determining initial resource level. 2. The giant rhinoceros beetle Trypoxylus dichotomus exhibits considerable variation in body size, some of which is attributed to the variation in larval food (humus) quality, although a substantial amount of variation in body size remains unexplained. In the present study, changes in the egg size and offspring body size in response to several maternal variables were examined (i.e. body size, age, and, nutritional status). 3. Nutritional intake of the females during the adult stage did not affect the egg size. Larvae hatched from small eggs partially recovered from the initial disadvantage during their ontogenetic processes by increasing growth rate (i.e. compensatory growth); however, there was still a positive relationship between egg size and pupal body size. 4. Older females produced small eggs, but because of compensatory growth, the pupae were no longer small. By contrast, due to a lack of compensatory growth, small females produced small eggs as well as small pupae. 5. These results suggest that maternal body size affects offspring body size through effects on egg size. This transgenerational effect may account for some of the variation in adult body size of T. dichotomus.     

Reproductive variation and the egg size-clutch size trade-off within and among populations of painted turtles (Chrysemys picta bellii)

Interpopulation variation in egg size, clutch size and clutch mass was studied 3 years in four populations of painted turtles (Chrysemys picta bellii) from western Nebraska. Body size varied among all populations and was larger in two large (56–110 ha), sandhills lake populations than in two populations in smaller habitats (1.5–3.6 ha) of the Platte River floodplain. Reproductive parameters (egg mass, clutch mass, and clutch size) generally increased with maternal body size within populations. Clutch wet and dry mass varied among populations but largely as a function of maternal body size. Clutch size was largest in the sandhills lake populations, both absolutely and relative to maternal body size. Egg mass was smallest in the sandhills lakes and varied annually in one population. Over all populations, an egg sizeclutch size trade-off was detected (a negative correlation between egg mass and clutch size) after statistically removing maternal body size effects. Egg wet mass and clutch size were negatively correlated over all years within the sandhills populations and in some years in three populations. Although egg size varied within populations, egg size and clutch size covaried as expected by optimal offspring size models. Thus, patterns of egg size variation should be interpreted in the context of proximate or adaptive maternal body size and temporal effects. Comparisons among populations suggest that large egg size relative to maternal body size may occur when juvenile growth potential is poor and mean maternal body size is small.